In recent years, active studies have been conducted on SON (Self Organizing Network), which autonomously optimizes radio parameters and network configurations in radio communication systems such as cellular systems, in view of operating expense (OPEX) reduction and the like. Standardization of SON functions is under way also in LTE (Long Term Evolution) of 3GPP (3rd Generation Partnership Project) (NPL 1).
SON includes functions such as:                Self-Configuration;        Self-Optimization;        Self-Healing.        
These are technologies for accomplishing respective different objectives. Of them, Self-Optimization includes categories such as: optimization of cell coverage and capacity (Coverage and Capacity Optimization: CCO); optimization of handover parameters (Mobility Robustness Optimization: MRO); and optimization of load balancing (Mobility Load Balancing: MLB) (NPL 2). Note that the term “CCO” is also used when only coverage optimization or capacity optimization is intended.
In SON, a problem is recognized by using radio quality information reported from terminals and communication quality statistical information compiled by a base station, and a radio parameter of the base station is autonomously optimized so that the problem will be improved. For the information reported from terminals, those prescribed in 3GPP are used, but many of current studies on SON employ radio quality measured by terminals in radio connected state (RRC Connected state).
On the other hand, 3GPP Release 10 newly prescribes MDT (Minimization of Drive Test) with the view of suppressing (minimizing) drive tests related to radio network operation management to the least extent possible. MDT prescribes an immediate reporting mode (Immediate MDT), in which a terminal in radio connected state performs measurement and reporting, and a recording and reporting mode (Logged MDT), in which a terminal in idle state (RRC Idle state) records a measurement result and reports it when it falls in radio connected state. Moreover, information to be measured includes not only radio quality information but also a measuring terminal's location information.
Accordingly, in SON, it is possible to optimize base station's parameters, based on radio quality information measured by terminals in immediate reporting mode or recording and reporting mode.
Moreover, PTL 1 discloses a method of performing parameter control based on an actual cell size. According to this parameter control method, in order to accurately estimate an actual cell size, a scheme is employed in which measurement information is aggregated for each of preconfigured divided areas and it is determined whether or not each area is within the radio area of a base station.